A recently completed systematic review identified the specific features of clinical decision support systems (CDSSs) that are most important for bringing about a desired change in clinical practice patterns. The objective of the proposed research is to apply the insights gained from this systematic review to design an XML-based CDSS, and to use this CDSS to improve the care of approximately 13,000 Medicaid benificiaries living in central North Carolina. The CDSS will support compliance with HEDIS guidelines for preventive and chronic care, and decision support communications will be provided to a variety of stakeholders, including clinicians, social workers, care managers, and patients. Of note, this work will leverage a number of existing resources established by this group, including a core XML-based decision support engine, a clinical database designed to support the care of Medicaid patients, and a touch-screen system for collecting information directly from patients. In building the CDSS, systems analysis techniques will be used to inform the design process, and a rapid prototyping approach will be used for system development. Then, a randomized controlled trial will be conducted to evaluate the impact of the CDSS, and outcomes will be measured using the HEDIS indicators for which the decision support was provided.